Paper towels, napkins or rags are known in the form of a continuous strip wound as a roll. Regularly spaced transverse perforation lines along this strip connect sheets which can be sequentially torn off. Each sheet therefore can be used individually. For high volume use, comparatively large rolls are housed inside cases. These cases are fitted with an element implementing cutting and feeding of a roll.
The present invention concerns centrally unwinding dispensers.
In such a system, a roll is operated without a spindle and the particular strip is pulled from its center through a feed element of small cross-section. Illustratively, this feed element assumes the shape of a hollow frustrum of a cone of which the minimum diameter extends outward. The strip enters the frustrum of a cone at its maximum diameter and is pulled out through the opposite orifice with the least diameter. This latter orifice causes some drag on the tension exerted by the user. The cross-section of the latter orifice is selected in such a manner that when the user pulls on the sheet, rupture occurs at the perforation line between a sheet already outside the cone and the next one still affixed inside. In this manner, one sheet is released after another. The force required to pull the strip through the cone is larger than the force needed to tear the sheets apart. Two consecutive sheets are reliably separated the moment the preceding one is wholly outside the cone.
Essentially the tear force required for the perforation lines is determined by two factors: the tear strength of the material to be dispensed and the percentage of bridge material left between the perforations of a line.
The removal force depends on several parameters:
surface condition, specific surface weight and thickness of the dispensed material, PA1 roll width, number of sheet plies; in particular the amount of material passing through the cone is directly proportional to the roll width, PA1 the cone material and its surface condition, and PA1 the diameter of the orifice at the exit of the cone.
With respect to the last parameter, U.S. Pat. No. 4,905,868 relates to a cone of a centrally feeding paper dispenser. Therein, the cone's exit orifice includes at least one detachable portion. In this manner, the exit orifice can be matched in particular to the paper thickness of two or three plies.
In U.S. Pat. No. 5,246,137, the size of the exit orifice is adjusted using appropriate inserts.
The frustoconical element undergoes substantial wear because of the abrasive nature of cellulose wadding. As the cross-section of an exit orifice increases, the friction opposing the sheet motion drops rapidly. A time comes when the user meets with less drag when pulling on the sheet. Then the sheet no longer will automatically rupture along the perforated line.
The dispenser's effectiveness is then much degraded. An insert such as cited in the above document might then be used to repair the cone. Another solution is offered in U.S. Pat. No. 5,310,083 wherein wear of the conical element is slowed by extending it with a cylindrical element. The sheet contacting surface in the area of high friction thereby being increased, wall wear is reduced.